Very slow import, plus missing skeleton.

[k-s-s]

I am currently using ue5 source to debug the issue, but had the same problem with 5.6.1 too. My Blender scene is two DAZ figures, each is in its own collection group, they are imported using Diffeomorphic. When pasting the import script into unreal engine, it takes 10+ minutes to import, and the second FBX fails to import a skeleton (The two figures have the same skeleton with slightly different proportions), in UE, it seems to pick the skeleton created from the first FBX. FBX 1: g9raw-base, 100k polygons, takes 11 minutes to load FBX 2: g9raw-base.001, 25k polygons, takes 37s to load, does not have it's own skeleton.

I tried different export procedures, UE FBX, Blender FBX and glTF. They were similar, I will run the glTF again, and provide an update. With UE FBX, I think the bulk of time was stuck in this area in UE:

Blender logs look good, no warnings or errors.

UE Logs:

[2025.10.31-20.57.35:529][526]Cmd: py "C:\Users\windows-user\Work\UE\MyGameData\MyGameData\Blender\Character\ExportedAssets\ImportAssetScript.py"
[2025.10.31-20.57.36:022][526]LogPython: # ==================== Import started ! ==================== #

[2025.10.31-20.57.36:033][526]LogPython: # ---------------------------------------------------------- #

[2025.10.31-20.57.36:046][526]LogPython: ### Import asset 1/2: 'g9raw-base'

[2025.10.31-20.57.36:063][526]LogPython: Target file: C:\Users\windows-user\Work\UE\MyGameData\MyGameData\Blender\Character\ExportedAssets\SkeletalMesh\g9raw-base\SKM_g9raw-base.fbx

[2025.10.31-20.57.36:071][526]LogPython: Task options: <Object '/Engine/Transient.InterchangeGenericAssetsPipeline_0' (0x00000277C4115400) Class 'InterchangeGenericAssetsPipeline'>

[2025.10.31-20.57.36:084][526]LogPython: Skeleton is not set, a new skeleton asset will be created...

[2025.10.31-20.57.36:215][526]LogStreaming: Display: FlushAsyncLoading(436): 1 QueuedPackages, 0 AsyncPackages
[2025.10.31-20.57.36:232][526]LogInterchangeEngine: Display: Interchange import: Using stack [OverridePipeline] to import.
[2025.10.31-20.57.36:234][526]LogInterchangeEngine: Display: Interchange start importing source [C:/Users/windows-user/Work/UE/MyGameData/MyGameData/Blender/Character/ExportedAssets/SkeletalMesh/g9raw-base/SKM_g9raw-base.fbx]
[2025.10.31-21.03.15:105][526]LogDerivedDataCache: ../../../Engine/DerivedDataCache: Maintenance finished in +00:00:00.002 and deleted 0 files with total size 0 MiB and 0 empty folders. Scanned 0 files in 1 folders with total size 0 MiB.
[2025.10.31-21.05.09:853][526]LogDerivedDataCache: //windows-user-pc/share/UE_DDC: Maintenance finished in +00:02:37.387 and deleted 123 files with total size 3 MiB and 103 empty folders. Scanned 211 files in 1439 folders with total size 7 MiB.
[2025.10.31-21.08.47:687][526]LogInterchangeImport: Translation (FBXSDK) of SKM_g9raw-base.fbx in [11 min 11.367 s]
[2025.10.31-21.08.53:226][526]LogAsyncCompilation: Display: AddQueuedWork [No DebugName] did not supply a RequiredMemory estimate. This is a bug, all asset types should provide an estimate. When no estimate is provided asset compilation is slowed as the queue has to operate very conservatively.
[2025.10.31-21.08.53:226][526]LogSkeletalMesh: Building Skeletal Mesh SKM_g9raw-base...
[2025.10.31-21.08.56:666][526]LogSkeletalMesh: Built Skeletal Mesh [3.44s] /Game/ImportedBlenderAssets/SKM_g9raw-base.SKM_g9raw-base
[2025.10.31-21.08.56:701][526]LogAsyncCompilation: Display: AddQueuedWork [No DebugName] did not supply a RequiredMemory estimate. This is a bug, all asset types should provide an estimate. When no estimate is provided asset compilation is slowed as the queue has to operate very conservatively.
[2025.10.31-21.08.56:718][526]LogSkinnedAsset: Display: Waiting for skinned assets to be ready 0/1 (SKM_g9raw-base) ...
[2025.10.31-21.08.57:046][526]LogWorld: UWorld::CleanupWorld for World_2, bSessionEnded=true, bCleanupResources=true
[2025.10.31-21.08.57:049][526]LogSlate: InvalidateAllWidgets triggered.  All widgets were invalidated
[2025.10.31-21.08.57:065][526]LogInterchangeImport: Imported (FBXSDK) of SKM_g9raw-base.fbx in [11 min 20.745 s]
[2025.10.31-21.08.57:065][526]LogInterchangeImport: MeshPayload (FBXSDK) of SKM_g9raw-base.fbx, [29 201248 2919604], in [0 min 1.254 s]
[2025.10.31-21.08.57:208][526]LogInterchangeEngine: Display: Interchange import completed [C:/Users/windows-user/Work/...letalMesh/g9raw-base/SKM_g9raw-base.fbx]
[2025.10.31-21.08.57:209][526]LogInterchangeEngine: Warning: [C:/Users/windows-user/Work/UE/MyGameData/MyGameData/Blender/Character/ExportedAssets/SkeletalMesh/g9raw-base/SKM_g9raw-base.fbx : 'SKM_g9raw-base', SkeletalMesh] Imported skeletal mesh has some invalid bind poses. Skeletal mesh skinning has been rebind using the time zero pose.
[2025.10.31-21.08.57:393][526]LogPython: Start rename skeleton...

[2025.10.31-21.08.57:766][526]LogFileHelpers: InternalPromptForCheckoutAndSave started...
[2025.10.31-21.08.57:954][526]LogFileHelpers: Saving Package: /Game/ImportedBlenderAssets/SK_g9raw-base_Skeleton
[2025.10.31-21.08.57:955][526]OBJ SavePackage: Generating thumbnails for [1] asset(s) in package [/Game/ImportedBlenderAssets/SK_g9raw-base_Skeleton] ([1] browsable assets)...
[2025.10.31-21.08.57:984][526]LogRenderer: Recreating Persistent SBTs due to initializer changes: 
		NumShaderSlotsPerGeometrySegment changed: current: 1 - new: 2
		NumGeometrySegments changed: current: 0 - new: 512
[2025.10.31-21.08.58:056][526]OBJ SavePackage:     Rendered thumbnail for [Skeleton /Game/ImportedBlenderAssets/SK_g9raw-base_Skeleton.SK_g9raw-base_Skeleton]
[2025.10.31-21.08.58:056][526]OBJ SavePackage: Finished generating thumbnails for package [/Game/ImportedBlenderAssets/SK_g9raw-base_Skeleton]
[2025.10.31-21.08.58:072][526]LogSavePackage: Moving output files for package: /Game/ImportedBlenderAssets/SK_g9raw-base_Skeleton
[2025.10.31-21.08.58:072][526]LogSavePackage: Moving '../../../../../Users/windows-user/Work/UE/MyGame/Saved/SK_g9raw-base_SkeletonE26E672A495722D9AF25CB823EA50C96.tmp' to '../../../../../Users/windows-user/Work/UE/MyGame/Content/ImportedBlenderAssets/SK_g9raw-base_Skeleton.uasset'
[2025.10.31-21.08.58:099][526]LogFileHelpers: InternalPromptForCheckoutAndSave took 334.436 ms
[2025.10.31-21.08.58:895][526]LogUObjectHash: Compacting FUObjectHashTables data took   7.98ms
[2025.10.31-21.08.58:977][526]LogUObjectHash: Compacting FUObjectHashTables data took   1.88ms
[2025.10.31-21.08.59:026][526]LogUObjectHash: Compacting FUObjectHashTables data took   1.01ms
[2025.10.31-21.08.59:037][526]LogPython: # ---------------------------------------------------------- #

[2025.10.31-21.08.59:041][526]LogPython: # ---------------------------------------------------------- #

[2025.10.31-21.08.59:052][526]LogPython: ### Import asset 2/2: 'g9raw-base.001'

[2025.10.31-21.08.59:066][526]LogPython: Target file: C:\Users\windows-user\Work\UE\MyGameData\MyGameData\Blender\Character\ExportedAssets\SkeletalMesh\g9raw-base.001\SKM_g9raw-base.001.fbx

[2025.10.31-21.08.59:078][526]LogPython: Task options: <Object '/Engine/Transient.InterchangeGenericAssetsPipeline_2' (0x00000280008AF300) Class 'InterchangeGenericAssetsPipeline'>

[2025.10.31-21.08.59:089][526]LogPython: Skeleton is not set, a new skeleton asset will be created...

[2025.10.31-21.08.59:211][526]LogInterchangeEngine: Display: Interchange import: Using stack [OverridePipeline] to import.
[2025.10.31-21.08.59:212][526]LogInterchangeEngine: Display: Interchange start importing source [C:/Users/windows-user/Work/UE/MyGameData/MyGameData/Blender/Character/ExportedAssets/SkeletalMesh/g9raw-base.001/SKM_g9raw-base.001.fbx]
[2025.10.31-21.09.37:018][526]LogInterchangeImport: Translation (FBXSDK) of SKM_g9raw-base.001.fbx in [0 min 37.782 s]
[2025.10.31-21.09.38:218][526]LogAsyncCompilation: Display: AddQueuedWork [No DebugName] did not supply a RequiredMemory estimate. This is a bug, all asset types should provide an estimate. When no estimate is provided asset compilation is slowed as the queue has to operate very conservatively.
[2025.10.31-21.09.38:218][526]LogSkeletalMesh: Building Skeletal Mesh SKM_g9raw-base_001...
[2025.10.31-21.09.39:085][526]LogSkeletalMesh: Built Skeletal Mesh [0.87s] /Game/ImportedBlenderAssets/SKM_g9raw-base_001.SKM_g9raw-base_001
[2025.10.31-21.09.39:094][526]LogAsyncCompilation: Display: AddQueuedWork [No DebugName] did not supply a RequiredMemory estimate. This is a bug, all asset types should provide an estimate. When no estimate is provided asset compilation is slowed as the queue has to operate very conservatively.
[2025.10.31-21.09.39:111][526]LogSkinnedAsset: Display: Waiting for skinned assets to be ready 0/1 (SKM_g9raw-base_001) ...
[2025.10.31-21.09.39:188][526]LogWorld: UWorld::CleanupWorld for World_4, bSessionEnded=true, bCleanupResources=true
[2025.10.31-21.09.39:188][526]LogSlate: InvalidateAllWidgets triggered.  All widgets were invalidated
[2025.10.31-21.09.39:194][526]LogInterchangeImport: Imported (FBXSDK) of SKM_g9raw-base.001.fbx in [0 min 39.959 s]
[2025.10.31-21.09.39:194][526]LogInterchangeImport: MeshPayload (FBXSDK) of SKM_g9raw-base.001.fbx, [29 50312 730278], in [0 min 0.338 s]
[2025.10.31-21.09.39:232][526]LogInterchangeEngine: Display: Interchange import completed [C:/Users/windows-user/Work/...lMesh/g9raw-base.001/SKM_g9raw-base.001.fbx]
[2025.10.31-21.09.39:232][526]LogInterchangeEngine: Warning: [C:/Users/windows-user/Work/UE/MyGameData/MyGameData/Blender/Character/ExportedAssets/SkeletalMesh/g9raw-base.001/SKM_g9raw-base.001.fbx : 'SKM_g9raw-base.001', SkeletalMesh] Imported skeletal mesh has some invalid bind poses. Skeletal mesh skinning has been rebind using the time zero pose.
[2025.10.31-21.09.39:425][526]LogPython: Error: export skeleton not found after import!

[2025.10.31-21.09.39:430][526]LogPython: Imported object paths:

[2025.10.31-21.09.39:444][526]LogPython:  - /Game/ImportedBlenderAssets/SKM_g9raw-base_001_PhysicsAsset.SKM_g9raw-base_001_PhysicsAsset

[2025.10.31-21.09.39:456][526]LogPython:  - /Game/ImportedBlenderAssets/SKM_g9raw-base_001.SKM_g9raw-base_001

[2025.10.31-21.09.39:479][526]LogPython: # ---------------------------------------------------------- #

[2025.10.31-21.09.39:482][526]LogPython: # ================ Full import completed ! ================ #

[2025.10.31-21.09.39:496][526]LogPython: Imported StaticMesh: 0

[2025.10.31-21.09.39:510][526]LogPython: Imported SkeletalMesh: 2

[2025.10.31-21.09.39:523][526]LogPython: Imported Alembic: 0

[2025.10.31-21.09.39:537][526]LogPython: Imported Animation: 0

[2025.10.31-21.09.39:549][526]LogPython: Import failled: 0

[k-s-s]

Further results: Reimport with same command: same time, 10min, 30s, second FBX does not import skeleton. Delete, create new export in Blender, import again: same time, 10min for FBX1, 30s for FBX2, FBX2 still no skeleton.

Delete, GLB export + import: GLB1 30s, GLB2: 8s, GLB2 still no skeleton

[xavier150]

Hello, regarding the skeleton, this is a bug in Unreal Engine. Unreal Engine assumes that both skeletal meshes should use the same skeleton. To resolve this issue, you need to import them into different folders.

About the slow time import sadly you need to check in the asset files what take time.